Fiber-reinforced molded plastic roofing unit and method of making the same

ABSTRACT

The present invention is directed to a molded roofing unit formed of a fiber-reinforced plastic composition configured to simulate the appearance of a conventional roofing product, such as a cedar shake, slate, or tile roofing product. The roofing product is configured to provide consistent results in the molding process, low material and production costs, high rigidity and strength, impact resistance, stability in high wind conditions, and ease of installation. In a preferred embodiment, the fiber-reinforced plastic composition is comprised of a polyolefin plastic compounded with at least partially delignified agricultural our forestry fibers. The roofing units possess high impact resistance, wind resistance and at least a Class C residential fire rating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally directed to the field of roofingmaterials and is more particularly directed to a molded roofing unitformed from a fiber-reinforced plastic, uniquely configured to simulateconventional roofing products and having high hail resistance, windresistance, fire resistance, ease of installation, and aesthetic appeal.

2. Description of the Related Art

A number of different roofing products have been developed and used overthe years to cover and protect a building. Various factors may beconsidered in choosing a roofing product including the cost of theproduct, ease of application or installation, and appearance. Equallyimportant is the performance or weatherability of the roofing product,meaning its ability to withstand cold, rain, hail and wind and to shedsnow and endure ice buildup without significant damage. Fire resistanceis another important consideration and is increasingly being identifiedby insurance companies as a desirable attribute for lowering insurancepremiums.

Clay tile, concrete, and slate roofs are distinctive and aestheticallypleasing in appearance such that even the "best" neighborhoodassociations approve the use of these roofing products. Clay, concrete,and slate also generally withstand wide ranging temperatures, rain, snowand wind, and are relatively fire resistant. However, these materialscan be expensive, may be susceptible to damage from hail and foottraffic, and the installment is generally labor intensive. Further,slate, concrete, and clay roofing products can be heavy, such thatreinforced structures may be required to support their weight.

Wood shakes are also generally approved by most neighborhoodassociations for residential use and are less expensive than clay,concrete, or slate roofs. Wood shakes are easier to install than clay,concrete, and slate roofs, although measuring and/or squaring of theindividual shakes during installation can prove time consuming and theshakes may split during shipment or installation, thereby increasing theoverall cost of materials. Wood shakes are also susceptible to haildamage and generally cannot attain a high degree of fire resistancewithout costly treatment. Wood shakes are often perceived as catchingfire relatively easily in the presence of lightening, sparks fromfireworks, or other airborne flames. When exposed to water, wood roofingmaterials may swell or curl along the edges, thereby providing aprotruding surface for winds to catch.

Asphalt shingles, also known as composition roofing, are less expensivethan wood roofing and are relatively easy-to-install. However, asphaltroofing products generally do not provide the sought after appearance ofwood shakes, slate, clay, or tiles, and therefore are not approved foruse in some residential areas with high-priced homes. While asphaltroofing is resistant to fire, it is generally prone to hail and winddamage and may need to be replaced over time due to brittling andcracking from exposure to the elements.

Due to the inadequacies of conventional roofing products, variousattempts have been made in the past to develop plastic-based roofingmaterials that possess the desired combination of physical properties,low cost, aesthetic appeal and ease of installation.

For example, U.S. Pat. No. 5,635,125 to Ternes et al. disclosesarelatively flat molded shingle formed of ground-up recycled polyvinylchloride (PVC) particles and wood sawdust particles. U.S. Pat. No.5,615,523 to Wells et al. discloses a relatively flat shingle panelcomprising a resinous plastic material combined with a large amount offiller.

While these prior plastic and/or composite roofing products heretoforedeveloped for replacing conventional roofing products are suitable forsuch purposes, none of the products developed to date have fully met thedesires of the industry. These prior products do not provide the desiredaesthetic attributes, nor superior physical properties. Thus, a needremains in the art for an improved plastic composite roofing productthat may be made from relatively safe polyolefin materials, recycledand/or virgin, having high impact resistance, wind resistance and fireresistance, with an aesthetically pleasing appearance and that may serveas a drop-in replacement for traditional roofing products at areasonable cost. To this end, one of the primary objects of thisinvention is to provide a polyolefin roofing unit reinforced bypartially delignified fibers, in which the fibers bind to the plastic toprovide a greater degree of wind resistance and impact resistance thanpreviously known in plastic roofing products and with costs comparableto traditional roofing products.

It is a further object of the invention to provide a lightweightfiber-reinforced plastic roofing composition and unit formed therefromof sufficient strength, stiffness, and impact resistance to withstandall types of outdoor conditions, including hail, high winds, and foottraffic.

It is yet another object of this invention to provide a fiber-reinforcedplastic roofing composition that can use post consumer and/or postindustrial plastics.

It is a further object of this invention to provide a fiber-reinforcedplastic roofing composition that uses waste agricultural and/or forestrymaterials.

It is another object of this invention to provide a fiber-reinforcedplastic roofing composition and unit formed therefrom with superiorproduct longevity over typical roofing materials.

It is a further object of this invention to provide a fiber-reinforcedplastic roofing unit with the appearance of slate, tile, or woodroofing.

It is another object of the invention to provide a fiber-reinforcedplastic roofing composition and unit formed therefrom that is resistantto pests.

It is still another object of the invention to provide afiber-reinforced plastic roofing composition and unit formed therefromof sufficient stiffness and strength to be installed on solid or spacedsheathing roof deck.

It is a further object of this invention to provide a fiber-reinforcedplastic roofing unit that can serve as a drop-in replacement for woodshake shingles.

It is still another object of this invention to provide afiber-reinforced plastic roofing unit with a configuration that providesincreased hail and wind resistance properties.

It is yet another object of this invention to provide a fiber-reinforcedplastic roofing unit that sheds snow and thereby reduces snow buildup.

It is still another object of this invention to provide afiber-reinforced plastic roofing unit that minimizes damage from icebuildup.

It is a further object of this invention to provide a fiber-reinforcedplastic roofing composition and unit formed therefrom that wicks littleor no water.

It is another object of this invention to provide a moldedfiber-reinforced plastic roofing unit that utilizes a minimal amount ofmaterials and that solidifies quickly after the molding process.

It is another object to create a fiber-reinforced plastic roofingcomposition and unit formed therefrom with greater solvent, detergent,and other chemical resistance than metal, PVC, or asphalt roofingproducts.

It is yet another object of this invention to provide a fiber-reinforcedplastic roofing composition and unit formed therefrom with a Class C orhigher fire rating.

It is a further object of the invention to provide a fiber-reinforcedplastic roofing unit that produces less waste in the creation andinstallation of the material as compared to cedar shakes.

It is still another object of the invention to provide afiber-reinforced plastic roofing composition and unit formed therefromwherein the reinforcing fiber is not highly abrasive.

It is yet another object of this invention to provide a fiber-reinforcedplastic roofing composition and unit formed therefrom with excellentnail-holding capacity.

It is yet another object of this invention to provide fiber-reinforcedplastic roofing composition and unit formed therefrom that is 100%recyclable.

It is yet another object of this invention to conserve the use ofindustrial resources.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved by a novel moldedroofing product and method of making the same wherein the product ismade from a fiber-reinforced plastic composition, is designed tosimulate conventional roofing such as wood shakes, slate, concrete, ortile and can be easily installed on the roof of a structure. The roofingproduct is uniquely configured to provide consistent results in themolding process, low material and production costs, high rigidity andstrength, impact resistance, stability in high wind conditions, ease ofinstallation and other functional advantages. The roofing product isinexpensive to manufacture and maintain, while having superior wind,hail and fire resistance over conventional roofing materials such ascedar shakes.

The roofing product consists of discrete roofing units which may beapplied to the roof of a building or other structure to protect thestructure from rain, snow, ice, wind, hail, sun, wildlife, and othernatural elements. The molded roofing units may be installed on the roofin a fashion similar to conventional asphalt shingles or wood shakeswherein the units are secured in place, one above the other, with nails,staples or screws.

The molded roofing units are formed from a fiber-reinforced plasticcomposition having impact resistance greater than 1.1 ft-lb/in to reducehail damage, superior flex modulus ranging from 275,000 to 600,000 psito withstand strong winds, and at least a class C fire rating to reducethe risk of fires.

The fiber-reinforced plastic composition preferably comprises a plasticcompounded with partially delignified agricultural or forestry fibersthat strongly bind to the plastic and thereby provide superiorreinforcement to the roofing product. The plastic is preferably selectedfrom one or more polyolefin plastics recycled from waste materials. Thepartially delignified fibers preferably are derived from fibers havingan aspect ratio (length to diameter×1,000 of the fiber) greater than 60,and most preferably greater than 100, to provide strength and stiffnessto the product.

In a preferred embodiment of the invention, a polyolefin plasticcomprised of cleaned waste plastics, such as high-density polyethylene(HDPE) and polypropylene, is compounded with partially delignifiedcellulosic fibers derived from waste forestry or agricultural materials,such as wheat straw, sugar cane bagasse, or wood cellulose. Thesecellulosic fibers may be partially delignified by any means known in theart to disrupt the lignin holding the individual fibers and fibrilstogether so as to increase the fiber surface area to which the plasticcan bond. Most preferably, the cellulosic fibers are delignified bysteam explosion, such as by the method described in U.S. Pat. No.5,705,216 to Tyson (hereinafter the "Tyson '216 Patent") or in U.S. Pat.No. 4,966,650 and Canadian Patents Nos. 1,141,376 and 1,096,374 toDeLong (hereinafter the "DeLong Patents"), in a manner to "open" theindividual fibers into an expanded fibrous micromesh matrix of fibrils,thereby enabling the plastic to flow into and bind with the fibers andfibrils. The fiber and fibril-plastic binding yields added strength,rigidity, and impact resistance, while providing resistance againstchemical attack, insect infestation, and frost damage. Optionally, thedelignified fibers may also be mechanically defibrillated to furtherdissociate the individual fibers and fibrils.

In addition to the polyolefin plastics, additional thermoplastics suchas nylons and engineered thermoplastic polyolefins (TPO) may be includedwithin the composition to increase the impact resistance and stiffnessof the roofing unit. It has also been found advantageous to incorporateadditives into the fiber-reinforced plastic composition to produceadditional desirable properties. Fire retardants such as aluminatrihydrate (ATH) may be added to achieve a fire rating superior to theClass C (residential) rating. Bonding agents such as Epolene may beadded to further enhance bonding of the fibers and plastic. Fillers maybe added to reduce the overall materials cost, and U-V protectants maybe added to prevent environmental stress cracking, discoloration,oxidation and to increase overall longevity. Further, a foaming agentmay be incorporated to enhance impact resistance and to reduce theweight of the roofing product and the volume of plastic required.

The molded roofing units are uniquely configured to simulateconventional roofing products such as wood shakes, slate, concrete, ortile, while providing consistent results in the molding process, lowmaterial and production costs, high rigidity and strength, impactresistance, stability in high wind conditions, ability to shed snow andminimize ice damage, resistance to water uptake, ease of installationand other functional advantages. Each roofing unit includes a generallyflat solid upper tab section intended to be secured to the roofstructure using nails, screws, staples or other conventional means, anda raised lower exposed section preferably having surface ridges or othertextural features to provide a desired appearance and functionaladvantages.

In a preferred embodiment, the top surface of the lower exposed sectionwill include relatively high and broad ridges configured to deflect andevenly distribute forces placed upon the unit, such as by hail,throughout a larger surface area of the unit, and valleys configured todirect water along the top surface of the unit and over its lower edge.While the lower exposed section is raised so as to appear relativelythick, adding dimension and texture to the roof when viewed from theground, the central underside of the exposed section includes a hollowcavity so as to reduce the materials cost and amount of cooling timeneeded when producing the molded unit. The hollowed cavity includes aseries of ribs that reinforce the unit and assist in evenly distributingany force placed upon the unit, such as by hail or foot traffic.

In a preferred embodiment, the molded unit has an upwardly arched shapeforming a camber along the midsection of the unit. When the tab sectionis nailed to the roof, both ends of the unit are held down by the slightstress resulting from the flattened camber, thereby preventing the endsof the unit from raising during high winds. An index line extendingtransversely across a midsection of the unit between the upper tabsection and the lower exposed section is also preferably included toassist the installer in accurately aligning and squaring the units inoverlapping relationship with one another.

In use, a first molded unit is squarely positioned on the roof structureso that the upper tab section is positioned above the lower exposedsection on the roof. The tab section is physically secured to the roofby securing nails, staples, screws or other conventional means throughthe tab section. A second molded unit may be secured in overlappingrelationship with the first unit by positioning the lower exposedsection of the second unit over the upper tab section of the first unit.These adjacent units may be more accurately and easily aligned bypositioning the bottom edge or end of the second unit along the indexline of the underlying first unit.

Although the following detailed description and drawings are directed toa preferred embodiment wherein the roofing unit simulates a conventionalcedar shake, the present invention may be applied to a variety ofroofing components, including units which simulate slate, tile, or otherroofing, as well as ancillary roofing components such as ridges, vents,and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a molded roofing unit in accordance withthe preferred embodiment of the present invention.

FIG. 2 is a top plan view of the molded roofing unit of FIG. 1.

FIG. 3 is a side view of the molded roofing unit of FIG. 1.

FIG. 4 is a butt end view of the molded roofing unit of FIG. 1.

FIG. 5 is a bottom plan view of the molded roofing unit of FIG. 1.

FIG. 6 is a cross sectional view taken along line 6--6 of FIG. 2.

FIG. 7 is a perspective partial view of a building roof with a pluralityof molded roofing units secured on the roof in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a molded roofing unit formed of afiber-reinforced plastic composition configured to simulate theappearance of a conventional roofing product, such as a cedar shake,slate, or tile roofing product.

Fiber-Reinforced Plastic Composition

The fiber-reinforced plastic composition utilized to form the roofingunit of the present invention has the combined characteristics of highimpact resistance, wind resistance and fire resistance, a combinationheretofore not achieved in conventional or plastic and/or compositeroofing materials at comparable prices of cedar shakes. The high impactresistance of the fiber-reinforced plastic is reflective of the highhail resistance of a molded roofing unit comprised of thefiber-reinforced plastic. The Izod impact rating of the fiber-reinforcedplastic ranges from 1.1 to 1.8 ft-lb/in, preferably greater than 1.2ft-lb/in, more preferably from 1.3 to 1.8 ft-lb/in, and most preferablygreater than 1.35 ft-lb/in, as measured by ASTM D256-93A.

The fiber-reinforced plastic composition of the present invention alsohas a flex modulus that can withstand most high winds to which it may beexposed on the roof of a structure. The fiber-reinforced plasticcomposition has a flex modulus rating ranging from 275,000 to 600,000psi, preferably between 300,000 and 375,000 psi, more preferably greaterthan 300,00 psi and most preferably ranging from 320,000 to 350,000 psi,as measured by ASTM D790-92.

In addition, the fire resistance rating of the fiber-reinforced plastic,as measured by ANSI/UL 790, generally ranges from Class A to Class C.Class C is the equivalent of a residential roofing rating. The preferredembodiment of the fiber-reinforced plastic that is molded into theroofing unit has at least a Class C fire rating.

A fiber-reinforced plastic composition consistent with the presentinvention will have additional benefits over previously known materialsutilized for roofing units. For example, a fiber-reinforced plasticconsistent with the present invention is naturally resistant to mostrodents and insects, including termites. In addition, thefiber-reinforced plastic can be produced at a reasonable cost relativeto other known plastic and/or composite materials utilized in formingroofing units. Further, the fiber-reinforced composition does not "wick"water and can therefore be used in lower pitched roofs than can cedarshakes.

The fiber-reinforced plastic composition preferably comprises apolyolefin compounded with partially delignified cellulosic fibers,wherein the fibers adhere to the polyolefin rather than serving merelyas a filler. The composition preferably comprises polyolefin in amountsranging from 50 to 80 percent by weight, and most preferably about 55 to65 percent by weight of the total composition. The compositionpreferably comprises partially delignified fiber in amounts ranging from20 to 50 percent by weight, and most preferably ranging from about 30 to45 percent by weight of the total composition.

Any moldable polyolefin or mixture of polyolefins may be used forpurposes of the present invention, including high and low densitypolyethylene, polypropylene, ionemers, other copolymers, includingengineered thermoplastic polyolefins (TPO), which may consist ofpolypropylene compounded with rubber. The polyolefin components arepreferably selected from the group consisting of HDPE and polypropylene,and most preferably from post consumer or post industrial wasteplastics, specifically waste HDPE, such as that reclaimed from used milkjugs. It should be apparent to one skilled in the art that virginplastic may be used equally effectively, although the benefit ofproductively utilizing waste plastic is then lost. By incorporating amixture of HDPE and polypropylene, little separation of the wasteplastic is required. Preferably the HDPE to polypropylene ratio isbetween 70:30 to 100:0 by weight of the total composition, and mostpreferably is from 85:15 to 100:0 by weight of the total composition.

The use of polyolefins in the molded roofing unit is preferable to theknown use of PVC in plastic and/or composite roofing materials.Polyolefins are relatively low cost thermoplastic materials that can beobtained in a host of grades and characteristics and are readilyavailable as recyclable waste materials. Polyolefins have relativelyhigh impact resistance and unlike PVC are not considered a potentialhealth risk.

The fiber utilized to reinforce the plastic comprising the moldedroofing unit of the present invention is a cellulosic fiber that hasbeen at least partially delignified so as to enhance bonding with theplastic. Any method for partially or fully delignifying cellulosicfibers so as to disrupt the lignin holding the fibers and the componentfibrils together is considered acceptable for purposes of thisinvention. A preferred method known for delignification includes steamexplosion, whereby the fibers separate and "expand" into a micromeshmatrix of fibrils as they are released from a high pressure steamchamber. Two steam explosion methods consistent with the preferredinvention are disclosed in U.S. Pat. No. 5,705,216 to Tyson (hereinafterthe "Tyson '216 Patent"), and in U.S. Pat. No. 4,966,650 and relatedCanadian Patents Nos. 1,141,376 and 1,096,374 to DeLong (hereinafter the"DeLong Patents"), each of which is hereby incorporated herein byreference. In addition, the partially delignified fibers can optionallybe mechanically fibrillated to further dissociate the individual fibersand fibrils as disclosed in the Tyson '216 Patent.

The fibers may be derived from agricultural or forestry fibers having anaspect ratio (length to diameter×1,000 of the fiber) greater than 60,preferably ranging from 60 to 150, more preferably 80 to 130, and mostpreferably near or above 100. The length of the fibers is an importantfactor in the aspect ratio and should exceed 1.0 mm, preferablyexceeding 1.5 mm. Small diameter fibers are preferable over thickfibers; fibers should be under 30 microns in diameter and preferablyunder 20 microns. Such fibers are preferably waste materials orbyproducts of other processes. The fibers may be selected from the groupconsisting of barley, wheat or rice straw, soy stalks, stalks ofperennial and annual grasses, sugar cane bagasse, kenaf, sawdust, otherforest product residues, and other plant materials. The most preferredfibers are wheat straw and sugar cane bagasse.

A wide variety of additives may be combined with the fiber and theplastic to enhance the properties of the molded roofing unit. Additivesconsistent with the invention include, but are not limited to, U-Vprotectants, impact modifies, fire retardants, bonding agents, colorantsand fillers. The additives, with the exception of impact modifiers,generally replace equal weight-percentages of fiber and polymer. Forexample, when a fire retardant is added in an amount equal to 30 percentby weight of the total composition, the percentages of fiber and polymerare decreased equally by 15 percent by weight of the total composition.Impact modifiers replace only plastic.

In the preferred embodiment of the invention, U-V protectants such asTinuvin 783 FB and/or Irganox B225F, both manufactured by Ciba Geigy,may be added to the composition in a total amount ranging from 0.3 to1.2 percent by weight of the total composition, with a preferred rangeof total U-V protectant of 0.8 to 1.0 percent by weight, and a mostpreferred amount of about 1.0 percent by weight. The U-V protectantscontrol cracking and minimize color changes resulting from exposure toultra-violet radiation. Although Ciba Geigy U-V protectants arereferenced for illustrative purposes, it will be recognized that othersuppliers offer similar products that serve similar functions.

Up to 30 percent by weight of the total composition may be comprised ofvarious impact modifiers selected from the group consisting of lowdensity polyethylene (LDPE), TPO, and nylons. These impact modifiers arepreferably added in amounts ranging from 0 to 30 percent by weight andmost preferably 10 to 15 percent. Impact-modifying polymers offer highresistance to impact, such as hail, and high resistance to environmentalstress cracking.

Bonding agents, such as Epolene, may be added to enhance bonding offibers and polyolefins in the range of 0 to 5 percent by weight of thetotal composition, with a preferred range of 2 to 3 percent.

Fire retardants may also be added in amounts up to 30 percent by weightof the total composition, with a preferred amount ranging from 16 to 24percent and a most preferred amount of approximately 20 percent byweight of the total composition, to achieve fire ratings in excess ofClass C (residential). The addition of 20 percent by weight of the totalcomposition of Micral 1500 ATH, a fire retardant sold by J. M. Huber,would be consistent with the present invention.

The natural color of the fiber-reinforced plastic of the preferredembodiment of the present invention is a gray color very similar to thecolor of an aged cedar shake. However, colorants can be added to producea product of a specific desired color. Conventional colorants dispersedin either polyethylene or polypropylene may be used, althoughadjustments must be made to compensate for the colors of the recycledplastic and fiber. One of ordinary skill in the art would be able tocalculate the amount and type of colorant necessary to produce a moldedroofing unit of a desired color without undue experimentation.Preferably the colorant is added in an amount ranging from 0 to 5percent by weight of the total composition.

Fillers, such as XPLE cable insulation produced by Alcan Aluminum, mayalso be added in amounts up to 15 percent by weight of the totalcomposition, more preferably between 3 and 10 percent by weight, toreduce the materials cost of the shake. Other thermoset plastic wastesmay also be used as fillers with some sacrifice of desired properties.

Polyethylene-compatible foaming agents, such Ready International'sSAFOAM-PE50, may also be added to the composition. The amount of foamingagent can range up to 3 percent by weight of the total composition,preferably about 1.5 percent. The foaming agent improves insulation andimpact resistance, reduces the weight of the roofing unit, reduces thecycle times and reduces the volume of polyolefin required forconstruction of the roofing composition. Weight reductions of 10 to 18percent may be achieved by the addition of a foaming agent.

Molded Roofing Unit Configuration

Turning to FIG. 1, a molded roofing unit in accordance with the presentinvention is generally designated by the numeral 10. Unit 10 is arelatively planar elongate shingle extending a length from an upper end12 to a lower butt end 14, having a top side 16 intended to faceoutwardly from the roof when installed, and an underside 18 intended toface inwardly toward the roof and rest flush against the roof and/orunderlying roofing unit when installed. The unit is preferablyintegrally formed within a mold as a single unitary piece offiber-reinforced plastic as heretofore described.

The roofing unit has a relatively thin flat upper tab section 20extending a length from upper end 12 to a lower tab end 22, and a lowerexposed section 24 extending a length from lower tab end 22 to butt end14. The overall length of the unit and of upper tab and lower exposedsections 20 and 24 will vary depending upon the desired appearance ofthe roofing unit. Preferably, upper tab section 20 is equal to orslightly greater in length than lower exposed section 24 so as toachieve complete overlapping coverage when installed on to the roof asdescribed below. Most preferably, upper tab section 20 will have alength ranging from 50 to 60 percent, and lower exposed section 24 willhave a length ranging from 40 to 50 percent, of the overall unit length.The transverse width of unit 10 will also vary depending upon thedesired appearance of the roofing unit, and the transverse width ofupper tab and lower exposed sections 20 and 24 will preferably be equalso as to achieve the desired overlapping coverage when installed on theroof.

In the case of simulated cedar shakes as shown in FIG. 1, unit 10 isgenerally rectangular in shape wherein the overall length of the unit isgreater than its transverse width. Preferably, the overall length of theunit ranges from 14 to 30 inches long, and most preferably ranges from21 to 25 inches in length. The transverse width of unit 10 preferablyranges from 4 to 16 inches, and is most preferably about 6 to 10 incheswide. Of course, it should be understood that different shapes anddimensions of roofing units are contemplated by the present invention.For example, a simulated slate roofing product may instead be relativelysquare in shape, or have a transverse width greater than the length ofthe unit, so as to accurately reflect the appearance of slate, forexample, when installed on the roof.

As best shown in FIG. 3, upper tab section 20 is formed as a relativelythin solid rectangular sheet of molded material. While the specificthickness of the tab section may vary depending upon the application, intypical roofing applications the tab section will have a thickness asmeasured from top side 16 to underside 18 ranging from 0.125 to 0.250inches. In a preferred embodiment, upper tab section 20 graduallydecreases in thickness from upper end 12 to lower tab end 22 such thattop side 16 of tab section 20 slopes downward at a slight angle overthis range, such that the thickness preferably decreases to 50 to 75percent of the thickness of upper end 12. This sloped design enables anoverlapping roofing unit to fit more securely over upper tab section 20when installed on the roof. When secured to the roof, the underside 18of tab section 20 is uniformly flat so as to rest flush against the roofand or/underlying unit when installed.

Looking to FIGS. 1, 3 and 6 lower exposed section 24 comprises a toppanel 26 of relatively uniform thickness having a top surface 28 and abottom surface 30. In a preferred embodiment, panel 26 is shaped toinclude a plurality of generally parallel longitudinal ridges 32 andvalleys 34 integrally formed within the panel to give top surface 28 thegeneral appearance of a natural cedar shake. It should be understoodthat panel 26 may be formed in a different shape and/or have differenttextural features depending upon the desired appearance of the roofingunit. For example, where a simulated clay tile is desired, panel 26 maybe formed as a smooth arched surface extending upwardly from lower tabend 22 to a central apex and downwardly to butt end 14. When a simulatedslate roof is instead desired, panel 26 may have a flaked slate surfacetexture with a rough or jagged outer edge along butt end 14. Thus, panel26 may be molded in any desired shape and with any desired texturalfeatures integrally formed therein.

In the preferred embodiment shown in the drawings, ridges 32 and valleys34 have an exaggerated height and width greater than that of a naturalcedar shake. Referring specifically to FIG. 6, ridges 32 have arelatively broad base b extending between low lying points of theadjacent valleys and relatively high peaks p extending above edge sidewalls 38 so as to deflect the force of any impact, such as by hail, anddistribute the force across a greater surface area of unit 10.Preferably, the height of peak p will be at least 0.275 the width of therespective base b of the ridge, and most preferably the peak to baseratio will be greater than 0.30.

Valleys 34 extend longitudinally and continuously along top panel 26 todirect water flow over the butt end 14 of unit 10. Preferably, theoutermost valleys are bordered by upwardly sloped border ridges 36 whichdirect water inwardly toward the outermost valleys so that water willnot flow off the sides of the unit. Most water from rain storms willtherefore be directed along the top surface 28 within border ridges 36of each unit and flow over butt end 14 to the lower exposed section 24of an underlying unit. The water will therefore be directed along aseries of valleys 34 contained in a series of roofing units down theroof until flowing over the lower edge of the roof into the gutteringsystem below.

Looking to FIGS. 3 and 6, edge sidewalls 38a and 38b of relativelyuniform thickness extend longitudinally along the sides of lower exposedsection 24 from lower tab end 22 to butt end 14. Edge sidewalls 38extend downwardly a height h from the bottom surface 30 of panel 26along its outer side edges at a generally perpendicular angle. Sidewalls38 gradually increase in height from lower tab end 22 to butt end 14such that top panel 26 is upwardly slanted at a relatively acute angletoward butt end 14. End wall 40 extends downwardly a height h from thebottom surface 30 of panel 26 along the butt end 14 at a generallyperpendicular angle.

The height of end wall 40 is at least equal to the maximum height ofsidewalls 38 such that the bottom edge of end wall 40 rests flush withthe bottom edge of adjacent sidewalls 38. Insofar as panel 26 is ofrelatively uniform thickness and shaped with ridges 32 and valleys 34,the upper edge of end wall 40 has corresponding ridges 42 and valleys 44extending above height h. In a preferred embodiment, the total height ofa peak, including height h of the endwall, the thickness of panel 26 andpeak height p, exceeds 90 percent of the width of base b. In thismanner, end wall 40, including ridges 42 and valleys 44, is ofsufficient height to be seen from ground level when installed on a roof.Furthermore, the upwardly slanted orientation of panel 26 and thedistinctive ridges and valleys formed therein give depth and texture tothe appearance of a roof comprising the roofing units.

Looking to FIGS. 5 and 6, top panel 26, edge sidewalls 38 and end wall40 together define a hollow cavity 46 on the underside 18 of lowerexposed section 24. Insofar as sidewalls 38 are formed integrally withtop panel 26 which is upwardly slanted toward end wall 40, cavity 46 isgenerally pyramidal in shape. By constructing unit 10 to include cavity46, unit 10 is constructed of less material than would be required for asolid unit, thereby reducing both material and production costs.Further, a unit containing cavity 46 cools more quickly than a solidunit, providing short cycle times and increasing consistency in thecharacteristics of the final molded product. Thus, a roofing unit isprovided which appears relatively thick from the ground, but is lessexpensive and more consistent in terms of quality than would be a solidthick molded unit.

To reinforce unit 10, a plurality of reinforcing ribs 48 are preferablyintegrally formed within cavity 46. Ribs 48 provide support to unit 10by evenly distributing any force, such as hail or foot traffic, acrossthe entire surface area of the unit. Ribs 48 extend downwardly frombottom surface 30 at a generally perpendicular angle into cavity 46 toform a grid-like pattern of ribs. This grid-like pattern is formed by aseries of ribs 48 extending across cavity 46 parallel end wall 40, and aseries of ribs 48 extending across cavity 46 parallel sidewalls 38.Other patterns of ribs forming multiple hexagons or triangles mayalternatively be used, but such configurations are generally moreexpensive to tool. The height of ribs 48 as measured from the bottomsurface 30 of panel 26 to the bottom of the ribs increases toward buttend 14, such that the bottom edges of the ribs rest flush with thebottom edges of sidewall 38 and end wall 40.

The intersection points 50 at which ribs 48 intersect are particularlysusceptible to stress and shear, the ends of the rib segments adjacenteach intersection point 50 are preferably built with a radius, meaningbuilt rounded to form reinforcing curvilinear rib walls 52 at theintersection points.

Looking to FIG. 3, unit 10 is slightly arched so as to form an upwardlyextending camber 54 along the midsection of unit 10. When roofing unit10 is nailed to a roof such that the cambered unit is flattened againstthe roof, and/or an underlying roofing unit, butt end 14 and upper end12 are held down against the roof by a slight generally downwardpressure resulting from the flattened camber 54. As a result of thepressure on ends 12 and 14, high winds generally will not raise the endsof the roofing unit. The force produced as a result of camber 54eliminates the need for additional interlocking features utilized insome known simulated roofing products to "lock" the edges of one unit toan adjacent unit so that the edges will stay flat against the roof Thus,camber 54 allows the unit 10 to be installed using a hammer and nails orstaple gun in the same manner as traditional cedar shakes. While theheight of the camber may vary, it is recommended that the camber height,as measured from a flat surface upon which the unit 10 is supported tounderside 18 of the unit at the camber apex, is at least 0.50 inches.

In a preferred embodiment shown in FIG. 1, upper tab section 20 andlower exposed section 24 are divided by index line 56 extendingtransversely across unit 10 adjacent lower tab end 22. Index line 56 maybe formed as a slightly raised or depressed groove within the top sideof the unit or may be formed by paint, ink or similar marking materials.As described below, index line 56 is useful in assisting the roofinginstaller to accurately align the roofing units in an overlappingrelationship. In use, the installer will position butt end 14 of a unit10, along the index line of an underlying unit so that the units areeasily squared and aligned.

EXAMPLE

A roofing unit 10 made in accordance with this invention has an overalllength of 22 inches extending from upper end 12 to lower butt end 14,and a uniform transverse width of 8 inches. Upper tab section 20 isabout 12 inches long extending from upper end 12 to lower tab end 22,and has a maximum thickness as measured from top side 16 to underside 18of about 0.200 inches at upper end 12. Upper tab section 20 decreasesslightly in thickness toward lower tab end 22 such that the top side 16slopes downwardly toward lower tab end 22 to a thickness of 0.135. Anindex line is formed as a straight groove extending transversely acrossthe top side 16 of the unit adjacent lower tab end 22.

Lower exposed section is about 10 inches long extending from lower tabend 22 to butt end 14. Top panel 26 extends from lower tab end 22 tobutt end 14 and has a relatively constant thickness of about 0.17 inchesadjacent lower tab end 22 increasing slightly to about 0.23 inchesadjacent butt end 14. Sidewalls 38 extend from lower tab end 22 to buttend 14 and increase in height from about 0.125 inches adjacent lower tabend 22 to about 0.20 inches adjacent butt end 14. The butt end wall 40similarly has a height of about 0.20 inches, excluding the thickness ofpanel 26 and the peak height p of ridges 42, such that when combinedwith the thickness of top panel 26, the average overall height of buttend 14 is about 0.43 (7/16) inches. The transverse width of sidewalls 38and end wall 40 is about 0.3 inches. Ridges 42 have an average peakheight of 0.20 inches or greater and ridge base of 0.60 inches orgreater. The peaks of the ridges are separated by no more than 1 inch.

Roofing unit 10 is arched along its length so as to form a camber 54along the midsection of the unit. The height of camber 54 as measuredfrom a flat surface upon which the unit may rest to the inner apex ofcamber 54 is at least 0.50 inch tall.

The combination of fiber-reinforced plastic with the uniquely configuredmolded unit results in a roofing unit having an impact resistance ratingranging from a Class 1 rating to a rating greater than Class 4, asmeasured by UL 2218. This high impact resistance rating equates to ahigh degree of hail resistance. In a preferred embodiment of theinvention, the molded roofing unit has an impact resistance rating inthe range of Class 2 to 4, with the most preferred embodiment achievingan impact resistance rating equal to or greater than Class 3.

The molded roofing unit of the present invention also has a high flexmodulus that provides a high degree of wind resistance to the roofingunit. A molded roofing unit consistent with the present invention canwithstand winds ranging from 80 to over 150 miles per hour (mph) astested by UL 997. The preferred embodiment of the unit can withstandwind speeds between 90 and 130 mph, and the most preferred embodimentcan withstand wind speeds of 110 mph and greater.

The molded fiber-reinforced plastic roofing product of the presentinvention has a fire resistance rating ranging from Class A to Class C,as measured by ANSI/UL 790. Class C is the equivalent of a residentialroofing rating. The preferred embodiment of the roofing unit has atleast a Class C fire rating.

Method for Making Molded Roofing Units

The preferred method for producing the molded roofing units of thepresent invention may be divided into a first phase of making thefiber-reinforced plastic composition and a second phase of producing themolded final product.

The method for making the fiber-reinforced plastic compositionpreferably comprises the steps of preparing the plastic, preparing thefibers, combining the plastic and fibers to produce fiber-reinforcedplastic pellets, and drying the pellets.

Preparation of the plastic includes selecting the plastics to beutilized, cleaning the plastic if recycled plastic is used and grindingthe cleaned plastic. When post consumer and/or post industrial plasticsare used, the polymers selected must be consistent in quality andcharacteristics and should be miscible, so that the molten polymers willflow together well and there will be no separation of polymers duringany phase of production. Differences in melting point between thevarious plastics used can create difficulties during processing of theplastic and can result in a non-uniform finished product. Specifically,one polymer may become overheated before another reaches a workable meltflow, leading to improper product formation or inconsistent physicalproperties in the final product. Shrinkage of the final product can alsooccur due to different polymer melt and flow rates thereby causingwarping, problems with ejection of parts from tooling and otherproblems. The melting points of the various plastics used preferablyrange between 5° and 75° F. and most preferably between 0 and 30° F. Themelt index of each is preferably within 1 to 25 percent of one anotherand most preferably within 0 to 10 percent.

Foreign matter should be removed before the plastic is processed,especially when waste plastics are selected for inclusion in thefiber-reinforced plastic composition. Washing of waste plastics enablesthe purchase of inexpensive uncleaned waste plastics for use in thecomposition. Magnetic or similar devices may be used to remove metalcontaminants. If not removed, metal contaminants can cause damage to theextruder and injection molding machines utilized in the productionprocess. Heavy contaminates may be removed by a wash system, screenpacks, and/or float sink operations.

The cleaned plastics are then ground to a size of under 0.75 (3/4) inchand preferably between 0.25 (1/4) and 0.50 (1/2) inch in both length andwidth. Oversized particles may be removed by passing the groundparticles through a classifier. The ground plastic is then stored untilit is combined with the treated fibers.

The process for preparing the fibers includes removing contaminants,grinding the fiber, partially delignifying the fiber and optionallyfurther treating the fibers to enhance bonding characteristics.Contaminants, such as metal, undesirable wood particles, plastic,stones, and dirt are removed from the fibers. As with the plastics,metal contaminants may be removed by magnetic devices to prevent damageto the extruders and injection molding machines. The clean fibers arethen ground to sizes ranging from 0.1 to 0.6 inch in length andpreferably being under approximately 0.375 (3/8) inch in length. Thegrinding may be accomplished using a tub grinder and/or a hammermill, orby any other means known in the art.

The fibers are then partially delignified to enhance their ability tobind to the polyolefin components of the composition. The preferredmethod of delignification utilizes a steam explosion process in whichthe individual fibers expand upon exiting the high pressure steamchamber as disclosed in the Tyson '216 Patent or in the DeLong Patents,each of which is incorporated herein by reference.

Although not wishing to be limited to any one theory, it is believedthat the steam explosion process disrupts the lignin-cellulose linkageswithin and between the fibers and partially disrupts the lignincontained therein. It is believed that the pressure differential betweenthe interior and exterior of the extruder barrel causes the fibers to"expand" rapidly as they exit the extruder. This expansion furtherdisrupts the lignin-cellulose linkages within and between the fibers,such that the individual cellulosic fibers separate and open into anexpanded micromesh matrix of cellulosic fibrils and micro fibrils,having a fiber surface area much greater than that of an untreatedlignocellulosic fiber. When the expanded fiber is mixed with thepolyolefin, the polymer is able to flow into the micromesh matrix andbond with the fibrils and microfibrils. Although the process partiallydelignifies the fibers, some lignin remains in the fiber and cannaturally adhere to the polyolefin.

The partially delignified fiber optionally may be further treated toenhance bonding characteristics, such as by neutralizing the pH of thefiber, drying the fiber, mechanically fibrillating the fiber, and/orincorporating a bonding agent such as Epolene. The preferred method ofneutralizing and drying is fully disclosed in the Tyson '216 Patent,incorporated herein by reference. The fibrillation step preferablycomprises running the fibers through a hammermill, a rotating drum dryerand /or any other known fibrillator to remove any lumps in the processedfiber and to achieve the desired fiber size. It is believed thatfibrillation dissociates and desegregates the individual fibers and thefibrils that form the micromesh matrix, thereby further increasing theamount of surface area that is available to bind with the polyolefin. Aswith the pre-processed fibers, the aspect ratio of the fibers should bebetween 60 and 100, more preferably between 80 and 130, and mostpreferably between 90 and 120. In a preferred embodiment, approximately75 percent of the processed fibers will pass through a 100 mesh screen.

The processed fiber and the plastic are compounded in an extrudercompounder. The desired amounts of the processed fiber, ground plastic,U-V protectants, bonding agent, and other additives, with the exceptionsof the foaming agent which is added later in the process may be fed intothe extrusion compounder. The components are preferably pre-dried in adesiccant dryer to a moisture content of less than 2 percent by weightof the total composition before feeding into a non-vented extruderbarrel. If the components are not so dried, a vented extruder barrelmust be used.

The barrel configuration includes a mixing screw with a length todiameter ratio of at least 28:1 and the extruder is preferably equippedwith a die to form strands. The screw has a mixing section in which thepolymers and fibers receive more shear and blending. Any suitableextruder known in the art that meets these specifications may beutilized to produce the fiber-reinforced plastic utilized in the presentinvention. The extruder may additionally comprise a blister pack locatedon the screw to pull volatiles from the compound, thereby reducing theamount of gas that is passed through to the end product.

The fiber-reinforced plastic composition exits the extruder in strandsthat must be cooled, dried, and cut to size. The cooled strands aredried to a moisture content of less than 11 percent by weight of thetotal composition with the preferred moisture content under 5 percent byweight of the total composition. The composition is then pelletizedusing any technique known in the industry that will produce pellets of aconsistent size, preferably approximately 0.125 (1/8) inch in diameterand less than 0.125 (1/8) inch in length. The fiber-reinforced plasticcomposition pellets may be shipped and/or stored for use in the secondmolding phase of the preferred process.

In the second phase of the preferred process, the final molded roofingunits are produced from the fiber-reinforced plastic composition. Thepreferred molding process comprises further drying the fiber-reinforcedplastic composition pellets, melting the composition in an injectionmolding machine, injecting the melted composition into roofing unitmolds, cooling the melted composition until at least partially hardenedsufficient to retain a shape, and removing the units from the molds.Optionally, the molded units may be only partially hardened in the moldand the partially hardened units may be placed on cooling fixtures,which fixtures may bend the units to produce a camber in the finalmolded roofing unit.

The composition pellets are preferably dried to a moisture content ofless than 2 percent unless a vented injection barrel will be used forthe injection molding or compression molding will be used. When anon-vented injection barrel is used, the moisture content of the pelletsis important. Failure to adequately dry the pellets, which have a highfiber content, may cause explosions in the barrel that may lead topre-ejection of hot plastic when the injection nozzle is not engagedwith the mold sprue or when the mold is open, or may lead to air pocketsin the final product.

The pellets are preferably dried in large desiccant dryers, although anysuitable dryer known in the art that will dry the composition to under 2percent moisture by weight may be employed. The temperature in thedryers is preferably kept between 175 and 250° F. At temperatures over250° F., the pellets will become hot enough to fuse together into lumps.When the temperature is below 175° F., the drying time is long,throughput is low, and, as a result, the cost of the processingincreases. A temperature range of 175 to 250° F. produces optimal energyoutput and minimal residence time to achieve the desired drying of thecomposition pellets.

The dried fiber-reinforced plastic composition pellets are preferablymelted and molded into a roofing unit of the desired configuration. Themolding process is preferably performed using injection molding,although utilizing non-pressurized melting followed by compressionmolding is also contemplated by this invention.

The dried fiber-reinforced plastic composition pellets are fed into aninjection molding machine. If colorant was not added during theextrusion step it may be fed into the injection molding machine with thecomposition pellets. Further, if a foaming agent is desired, it is alsometered into the throat of the injection molding machine with thecomposition pellets, preferably using a ratio loader such as Model SRL-1produced by Plasti-Equip.

Consistent with the preferred method, injection molding machines may beused in conjunction with multi-cavity molds, and preferably amulti-cavity stacked mold is used to exploit the economies of scaleprovided by such molds. However, the roofing unit may be constructedusing a single cavity conventional mold or any other suitable mold typeknown in the art.

The barrel temperature of the injection molding machine, as well as thetemperature of the fiber-reinforced plastic composition, must bemaintained between 325° and 393° F. and most preferably between 340° and390° F., the narrow temperature range in which the plastic, the fibers,and any added fire retardant are thermally stable. The fire retardantATH loses its fire resistance properties at 393° F., and at temperaturesover 400° F., the fiber begins to degrade. Degradation of the fiber willlessen the amount of reinforcement provided to the roofing unit.Further, fiber degradation generates volatile gases, thereby producingresults similar to those produced by the use of composition pelletshaving greater than 2 percent moisture, discussed above.

In a preferred method, the various zones of the injection molding barrelhave different temperatures. The rear zone of the barrel, through whichthe composition first passes, has temperatures ranging from 325 to 390°F., with the preferred temperature ranging from 350 to 370° F. Themiddle zone of the barrel has temperatures ranging from 335 to 390° F.,with the preferred temperature ranging from 355 to 375° F. The frontzone of the barrel has a preferred temperature range from 325 to 390°F., similar to the rear zone of the barrel. The nozzle of the injectionmolding apparatus, adjacent the front zone of the barrel, o has apreferred temperature in the range of 330 to 390° F., with a morepreferred temperature ranging from 350 to 380° F. Finally the mold intowhich the melted composition is injected is much cooler, having apreferred temperature range from 60 to 135° F., with the more preferredtemperature ranging from 95 to 115° F.

The narrow range of operating temperatures precludes use of a number ofpolymers, such as ABS, some nylons, polyamide-ide, polycarbonate, manypolyesters, and polyethylene terephthalate (PET). Care must be exercisedto keep the composition within the desired temperature range, not justthe barrel. For example, when filling multi-cavity molds, large amountsof composition are injected. If injection occurs too rapidly (over 80ounces of composition in less than 10 seconds) excess mechanical heatmay be generated and the composition will scorch.

On the other hand, the injection speed must be relatively fast,preferably filling roughly 6.5 ounces per second, in order to allow thethin end of the mold (e.g. the upper tab section 20) to completely fillbefore hardening of the composition in the mold begins. The mold ispreferably fan-gated on the side, thereby orienting most of the fibersalong the exposed portion of the roofing unit, parallel to thelongitudinal axis of the unit, to provide the desired mechanicalproperties. Other gating known in the art to achieve this preferredfiber orientation may be used.

The mold can be designed to construct a roofing unit similar inappearance to a cedar shake, slate, tile, or any other suitableconfiguration, while incorporating other functional and cost effectivefeatures, as described above. The mold design is critical to both thefinal shape of the product and to the cycle times. The mold alsocontains cooling passages, which will be known by those of ordinaryskill in the art to be channels through which cold water flows to removeheat from the molded product, thereby decreasing the time required forthe composition to set, and allowing the finished product to be removedfrom the mold rapidly while retaining its shape.

The mold is constructed to provide a molded roofing unit productconfigured as described earlier above. While the cavity 46 in theunderside of roofing unit 10 serves to reduce the cooling time of thethicker lower exposed section 24, the lower exposed section stillrequires more cooling time than the thinner upper tab section 20. Theconfiguration of water cooling passages must be designed to account forthis difference in thickness as well as the pattern of ribs 48 withincavity 46. The cooling passages are preferably constructed to removemore heat from the thick lower exposed section 24 than from the thinupper tab section 20, thereby producing a uniformly cooled product.

In a preferred embodiment, the roofing unit is removed from the moldwhen the, unit has sufficiently hardened to retain its molded shape, butbefore the unit has fully hardened. The partially hardened unit istransferred directly to a cooling fixture that is designed to preventthe unit from warping and twisting so as to maintain the shape of theunit until the composition is fully hardened and cured. In the preferredembodiment, the fixtures hold the unit from the time it is removed fromthe mold until the unit is completely cooled and hardened. The fixturescontribute to short cycle times by allowing the unit to be removed fromthe mold before it is completely cooled and hardened. Shorter cycletimes decrease the costs of production since more units can be producedin a shorter time.

Additionally, in a preferred embodiment the fixtures are constructed toslightly bend the midsection of the roofing unit 10 during cooling toproduce camber 54 near the midsection of the roofing unit. In one methodconsistent with the present invention, the fixture holds the upper tabsection 20 of the unit while allowing the lower exposed section 24 tohang over the edge of the fixture, thereby creating a bend, or camber,in the unit. Of course, it should be understood that other means knownin the art for bending or arching a molded product may alternatively beused to produce the camber 54. Alternatively the camber may be builtinto the mold or may be created by the arrangement of the shakes whenbundled together for shipment and storage.

Method of Installing the Molded Roofing Unit

A roofing unit consistent with the present invention can be affixed to aroof in the same general manner as a conventional roofing unit isinstalled. The roof surface on which the roofing units are installed istypically interlaced with Type 30 felt paper and no underlayment isrequired. Due to the stiffness of the molded roofing unit, roofing unitsconsistent with the present invention may be applied on spaced sheathroofing or solid decking. Further, unlike cedar shakes, nails should notsplit the molded roofing units of the current invention, therebyreducing waste resulting from discarded broken roofing units. The nailholding capacity of the fiber-reinforced plastic composition is superiorto that of wood shakes and other known plastic and/or composite roofingcompositions and therefore the units are more resistant to high winds.Additionally, the inherent nature of polyethylene to "creep," or settle,causes the roofing unit of the present invention to "self seat". As thepolyethylene creeps, it settles onto itself rather than drooping on thesides, thereby adding to the stability of the unit on the roof.

Index line 56, a reference mark on the roofing unit, further increasesthe ease of installation. Cedar shakes and most other non-plasticproducts do not contain such a line. Looking to FIG. 7, to installroofing units containing such an index line, the roofer begins byinstalling a plurality of roofing units in a first row along the lowestedge of the roof. A second upper row, comprising a plurality of roofingunits, is then installed such that lower exposed sections 24 of theroofing units of the second upper row are placed in an overlappingrelationship with upper tab section 20 of the roofing units of the firstrow. The upper row is installed such that lower exposed sections 24cover the upper tab sections 20 of the first row. The third row isinstalled in the same manner as the second, and additional rows aresimilarly installed until the roof is covered. After all roofing unitsare installed, butt ends 14 and top surfaces 28 of lower exposedsections 24, including any ridges and valleys, of nearly all of theroofing units are visible to a person standing on the ground, providingan aesthetically pleasing appearance.

The roofer uses index line 56 to determine the correct amount of overlapbetween rows of roofing units and to keep the roofing units runningsquare on the roof. Using the index line, the roofer merely installs theupper row of roofing units so that the butt end 14 of the upper roofingunits just cover the index line of the roofing units comprising the rowbelow. As a result, the upper row of roofing units is parallel to thelower index line across the entire length of the roof producing aprofessional appearance. Without this index line, roofers must eithermeasure and square each roofing unit or estimate the length of exposureand the square placement of the units.

Use of a fiber-reinforced plastic molded roofing unit consistent withthis invention produces less waste than use of cedar shakes due to a lowoccurrence of splitting of the plastic during shipment and installation.Further, because the roofing units are molded, they contain fewimperfections and nearly all of the molded roofing units that areproduced are useable and of a correct size. Finally, because the moldedroofing units are recyclable, any waste that is produced may be groundand reused to produce new molded roofing units. Such waste reduction isvery desirable and conserves natural resources.

In one embodiment of the present invention described above, the roofingunits are generally shaped like a cedar shake. Not only are thesimulated shakes drop-in replacements for cedar shakes with respect toinstallation, but the appearance, packaging, shipping, palleting, andbundling are already well known to roofers. In addition, because theshakes of the present invention are more durable than cedar shakes, fewshakes are damaged during loading and shipping thereby reducing wasteover cedar shakes which readily split during shipment and installation.

The preferred embodiments directed to cedar shakes with magnified ridgesdescribed above are illustrative only. Numerous changes, modifications,and alterations will be contemplated by those skilled in the art withoutdeparting from the spirit and scope of the novel concept of thisinvention. For example, other methods for producing the fiber reinforcedplastic composition and/or roofing unit are contemplated by thisinvention. Furthermore, roofing units of different configuration havingthe claimed features are contemplated in this invention. The scope ofthe invention is limited only by the appended claims and anymodifications within the scope of the claims.

What is claimed is:
 1. A roofing product for use in covering the roof ofa structure, said product comprising:a molded roofing unit formed from afiber-reinforced plastic composition, wherein said composition iscomprised of a polyolefin and cellulosic fibers, said cellulosic fibershaving been partially delignified so as to sufficiently disrupt ligninbinding individual fibrils of said cellulosic fibers to enable saidpolyolefin to flow between and bind to said individual fibrils.
 2. Theroofing product of claim 1, wherein said plastic composition has animpact resistance greater than 1.2 ft-lb/in, a flex modulus greater than300,000 psi, and a fire resistance rating of at least Class C.
 3. Theroofing product of claim 1, wherein said composition comprises saidpolyolefin in amounts ranging from 50 to 80 percent by weight of thetotal composition.
 4. The roofing product of claim 1, wherein saidpolyolefin is selected from the group consisting of high densitypolyethylene, medium density polyethylene, low density polyethylene,polypropylene, ionemers, engineered thermoplastic polyolefin (TPO) andcompounds of each.
 5. The roofing product of claim 3, wherein saidcomposition comprises fibers in amounts ranging from 50 to 20 percent byweight.
 6. The roofing product of claim 1, wherein said fibers are atleast partially delignified by steam explosion.
 7. The roofing productof claim 6, wherein said fibers have additionally been mechanicallyfibrillated to dissociate individual fibers and component fibrils. 8.The roofing product of claim 1, wherein said fibers have an aspect ratio(length to width) greater than
 60. 9. The roofing product of claim 1,wherein said fibers are selected from the group consisting ofagricultural and forestry fibers.
 10. The roofing product of claim 1,wherein said composition additionally comprises a bonding agent.
 11. Theroofing product of claim 1, wherein said composition additionallycomprises an ultra-violet protectant.
 12. The roofing product of claim1, wherein said composition additionally comprises an impact modifier.13. The roofing product of claim 1, wherein said molded roofing unit isrelatively planar having a top side intended to face outwardly of theroof of a structure and an underside intended to face inwardly restingin abutting engagement with the roof, the distance between said top sideand said underside being the thickness of the unit at any given locationalong a length of said unit, and wherein said unit comprises:arelatively thin upper tab section extending from an upper end of theunit to a lower tab end, and a lower exposed section extending from saidlower tab end to a lower butt end of the unit, wherein said lowerexposed section increases in thickness from said lower tab end to saidbutt end.
 14. The roofing product of claim 13, wherein said upper tabsection decreases in thickness from said upper end to said lower tabend.
 15. The molded roofing unit of claim 13, wherein said roofing unitis integrally formed within a mold as a single unitary piece offiber-reinforced plastic.
 16. The molded roofing unit of claim 13,wherein said lower exposed section comprises:a top panel extendinglongitudinally from said lower tab end to said butt end, said top panelhaving a top surface to define the top side of the unit within the lowerexposed section, a bottom surface and side edges, edge sidewallsextending downwardly from the side edges of the panel, and an end wallextending downwardly from the panel along the butt end of the unit,wherein said top panel, said edge sidewalls and said end wall define acavity on the underside of said unit within the lower exposed section.17. The roofing product of claim 16, wherein a bottom edge of said endwall and a bottom edge of each of said edge sidewalls rest in the sameplane so as to lie flush against the roof of the structure when theroofing product is secured to the roof.
 18. The roofing product of claim16, wherein said molded roofing unit further comprises a plurality ofreinforcing ribs formed within said cavity.
 19. The roofing product ofclaim 18, wherein a bottom edge of each of said ribs rest in the sameplane as the bottom edges of said edge sidewalls and end wall so as tolie flush against the roof of the structure when the roofing product issecured to the roof.
 20. The roofing product of claim 18, wherein saidribs are curved at their intersection points to reinforce saidintersection points.
 21. The roofing product of claim 13, wherein saidroofing unit is arched to form a camber along the length of said unit.22. The roofing product of claim 13, further comprising an index lineextending transversely across said unit adjacent said lower tab end. 23.The roofing product of claim 13, wherein said molded roofing unit isshaped to include a plurality of generally parallel longitudinal ridgesand valleys.
 24. A roofing unit for securing to a roof of a structure tocover and protect the roof of the structure, wherein said roofing unitextends longitudinally from an upper end to a lower butt end andcomprises:a top side intended to face outwardly of the roof when securedto the roof, an underside intended to face inwardly resting in abuttingengagement with the roof when secured to the roof, the distance betweensaid top side and said underside being the thickness of the unit at anygiven location along a length of said unit; a solid upper tab sectionextending from the upper end of the unit to a lower tab end, wherein thethickness of the upper tab section decreases from the upper end to thelower tab end to define a downwardly sloping top side of the unit withinthe upper tab section; a top panel extending from said lower tab end tothe butt end of the unit, to form a lower exposed section said top panelhaving a top surface, a bottom surface and side edges; a plurality oflongitudinal ridges and valleys formed within the top panel of the unit;edge sidewalls extending downwardly from the side edges of the panel toa bottom edge of the sidewalls, wherein a height of said edge sidewallsincreases from said lower tab end to said butt end of the unit; an endwall extending downwardly from the panel along the butt end of the unitto a bottom edge of the end wall; a cavity on the underside of the unitwithin the lower exposed section; a first set of ribs extending parallelto said edge sidewalls within said cavity; a second set of ribsextending parallel to said end wall within said cavity such that saidfirst and second sets of ribs form a grid of intersecting ribs withinsaid cavity, wherein a bottom edge of each of said ribs, the bottom edgeof each of said edge sidewalls and the bottom edge of the end wall arein the same plane so as to rest flush against the roof of the buildingwhen the roofing unit is secured to the roof; a camber formed along thelength of said unit such that the unit is arched along a midsection ofthe unit; and an index line extending transversely across said unitadjacent said lower tab end.
 25. The roofing unit of claim 24 whereinsaid roofing unit is formed from a fiber-reinforced plastic compositioncomprising a polyolefin blended with cellulosic fibers that are at leastpartially delignified.
 26. A roofing unit as claimed in claim 24 whereinsaid longitudinal ridges have a base and a peak and wherein a ratio of aheight of said peak to a width of said base is greater than 0.30.